1. Field of the Invention
Exemplary embodiments of the present patent application relate to a sheet feeding device and an electrophotographic image forming apparatus incorporating the sheet feeding device, and more particularly, to a sheet feeding device that electrostatically attracts a sheet of a recording medium to an endless belt member for separating and feeding the sheet therefrom, and an electrophotographic image forming apparatus incorporating the sheet feeding device.
2. Discussion of the Related Art
Related-art image forming apparatuses, such as electrophotographic copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a sheet of recording media according to image data. Thus, for example, a sheet feeding device loads a plurality of sheets and feeds the plurality of sheets one by one toward an image forming device. The image forming device forms an image on a sheet supplied from the sheet feeding device.
As one approach, an electrostatic sheet feed method to separate and feed a sheet electrostatically has been proposed.
The electrostatic sheet feed method is employed in a sheet feeding device that can be incorporated in an electrostatic image forming apparatus. The sheet feeding device includes an endless dielectric belt member and a charging member for charging and discharging the surface of the endless dielectric belt.
The endless dielectric belt member that rotates in a sheet feed direction contacts a top surface of a stack of sheets, and the charging member applies alternating charges (that is, electrical charges of alternating polarity) to the surface of the endless dielectric belt member. The charging member performs both a charging operation to form an alternating charge pattern on the surface of the endless dielectric belt member and a discharging operation to discharge or remove the charge from the surface of the endless dielectric belt member. Application of electric charge to the endless dielectric belt member to contact the endless dielectric belt member to the sheet increases the electric potential of the sheet and causes oppositely polarized electric charges to generate a force of attraction. This action can separate an uppermost sheet from the stack of sheets and feed the uppermost sheet in a sheet conveyance direction.
As another example of an electrostatic sheet feed method, JP 2003-237958 discloses a sheet feeding device that includes a belt unit including an endless belt and a charging roller. The endless belt is looped over a drive roller and a driven roller to rotate according to rotation of the drive roller. The charging roller applies an electric charge to an outer surface of the endless belt. The belt unit is driven by a swing motor.
In the sheet feeding device as disclosed in JP 2003-237958, when the charging roller forms an alternating charge pattern on the outer surface of the endless belt, the swing motor drives the belt unit to move from a home position of the belt unit to a position close to the uppermost sheet along an axial direction of the drive roller. Thus, the endless belt contacts the uppermost sheet placed on top of the stack of sheets and attracts the uppermost sheet.
After a given period of time has elapsed to separate the uppermost sheet from the stack of sheets with the endless belt attracting the uppermost sheet, the swing motor moves the belt unit back to the home position. Thus, the uppermost sheet separates from the other sheets of the stack of sheets.
As another approach, JP 2009-023813 discloses a different electrostatic sheet feeding device. The electrostatic sheet feeding device disclosed in JP 2009-023813 includes a sheet stacker that accommodates multiple sheets, a sheet feeding roller that contacts a top surface of the multiple sheets accommodated in the sheet stacker and feeds an uppermost sheet placed on the multiple sheets in a sheet feeding direction, a separation pad, an electrostatic sheet attraction unit disposed upstream from the position of the sheet feeding roller in the sheet feeding direction that electrostatically attracts the uppermost sheet, and a driving unit to swing the electrostatic sheet attraction unit in a substantially vertical direction.
The electrostatic sheet attraction unit includes two rollers and an electrostatic attraction belt that is looped over the two rollers. A charging roller is disposed in a vicinity of the electrostatic attraction belt to apply an alternating voltage to the electrostatic attraction belt to electrostatically charge the electrostatic attraction belt.
The driving unit includes a drive shaft that is disposed opposite the sheet feeding roller with the sheet stacker interposed therebetween and a supporting arm that is pivotably supported by the drive shaft. The electrostatic sheet attraction unit moves in a substantially vertical direction about the drive shaft via the supporting arm.
In the sheet feeding device as disclosed in JP 2009-023813, the driving unit swings the electrostatic sheet attraction unit downward to contact the uppermost sheet of the stack of sheets. With this action, the electrostatic attraction belt that is charged by the charging roller attracts the uppermost sheet. As the supporting arm moves in an upward direction, the electrostatic sheet attraction unit is elevated to a predetermined level of height to separate the uppermost sheet attracted by the electrostatic attraction belt from the stack of sheets.
However, to achieve the above-described operation, the sheet feeding device disclosed in JP 2003-237958 requires the swing motor to swing the belt unit between the home position and a position close to the uppermost sheet when performing an attracting operation and a separating operation. Use of such a swing motor complicates construction and increases the cost of the sheet feeding device.
The sheet feeding device as disclosed in JP 2009-023813 requires the driving unit including the supporting arm to swing the electrostatic sheet attraction unit in a substantially vertical direction when attracting and separating the sheet. As a result, similar to JP 2003-237958, installation of the driving unit complicates construction and increases the cost of the sheet feeding device.